Devices and methods for cooling microwave antennas

ABSTRACT

Devices and methods for cooling microwave antennas are disclosed herein. The cooling systems can be used with various types of microwave antennas. One variation generally comprises a handle portion with an elongate outer jacket extending from the handle portion. A microwave antenna is positioned within the handle and outer jacket such that cooling fluid pumped into the handle comes into contact directly along a portion of the length, or a majority of the length, or the entire length of the antenna to allow for direct convective cooling. Other variations include cooling sheaths which form defined cooling channels around a portion of the antenna. Yet another variation includes passively-cooled systems which utilize expandable balloons to urge tissue away from the surface of the microwave antenna as well as cooling sheaths which are cooled through endothermic chemical reactions. Furthermore, the microwave antennas themselves can have cooling lumens integrated directly therethrough.

The present application is a Continuation Application that claims thebenefit of and priority to U.S. application Ser. No. 11/940,738, filedNov. 15, 2007, now U.S. Pat. No. 9,468,499, which is a continuation ofU.S. application Ser. No. 10/622,800, filed on Jul. 18, 2003, now U.S.Pat. No. 7,311,703, both of which are incorporated herein by referencein their entirety.

FIELD OF THE INVENTION

The invention relates generally to microwave antennas which may be usedin tissue ablation applications. More particularly, the inventionrelates to devices and methods for reducing or maintaining temperaturesof microwave antennas used in such applications.

BACKGROUND OF THE INVENTION

In the treatment of diseases such as cancer, certain types of cancercells have been found to denature at elevated temperatures which areslightly lower than temperatures normally injurious to healthy cells.These types of treatments, known generally as hyperthermia therapy,typically utilize electromagnetic radiation to heat diseased cells totemperatures above 41° C. while maintaining adjacent healthy cells atlower temperatures where irreversible cell destruction will not occur.Other procedures utilizing electromagnetic radiation to heat tissue alsoinclude ablation and coagulation of the tissue. Such microwave ablationprocedures, e.g., such as those performed for menorrhagia, are typicallydone to ablate and coagulate the targeted tissue to denature or kill it.Many procedures and types of devices utilizing electromagnetic radiationtherapy are known in the art. Such microwave therapy is typically usedin the treatment of tissue and organs such as the prostate, heart,kidney, lung, brain, and liver.

Presently, there are several types of microwave probes in use, e.g.,monopole, dipole, and helical, which may be inserted into a patient forthe treatment of tumors by heating the tissue for a period of timesufficient to cause cell death and necrosis in the tissue region ofinterest. Such microwave probes may be advanced into the patient, e.g.,laparoscopically or percutaneously, and into or adjacent to the tumor tobe treated. The probe is sometimes surrounded by a dielectric sleeve.

However, in transmitting the microwave energy into the tissue, the outersurface of the microwave antennas typically may heat up andunnecessarily necrose healthy tissue immediately adjacent the antennaouter surface. To prevent the charring of adjacent tissue, severaldifferent cooling methodologies are conventionally employed. Forinstance, some microwave antennas utilize balloons which are inflatablearound selective portions of the antenna to cool the surrounding tissue.Thus, the complications associated with tissue damaged by theapplication of microwave radiation to the region is minimized.Typically, the cooling system and the tissue are maintained in contactto ensure adequate cooling of the tissue.

Other devices attempt to limit the heating of tissue adjacent theantenna by selectively blocking the propagation of the microwave fieldgenerated by the antenna. These cooling systems also protect surroundinghealthy tissues by selectively absorbing microwave radiation andminimize thermal damage to the tissue by absorbing heat energy.

However, in order for microwave ablation to become a truly effectivetool for the laparoscopic and/or percutaneous treatment of tumors, aneffective microwave antenna should be implemented to efficientlytransfer energy to the targeted tissue region while minimizingunnecessary tissue damage adjacent to the antenna outer surface.Moreover, the cooling aspects along the antenna should be controllableto allow for different regions of cooling as well as to allow for thecoagulation of adjacent tissue along selected regions of the antenna, ifdesired.

BRIEF SUMMARY OF THE INVENTION

In minimally invasively treating diseased areas of tissue in a patient,trauma may be caused to the patient resulting in pain and othercomplications. One cause of trauma may result from excess tissue beingunnecessarily ablated by the microwave antenna assembly. As themicrowave antenna transmits microwave energy, the feedline or shaft ofthe antenna may increase in temperature and the contacting tissue maybecome charred or ablated unnecessarily. Moreover, charred tissue maydecrease the effectiveness of the microwave antenna. The coolingsystems, as described herein, may be used in conjunction with varioustypes of microwave antennas, e.g., antennas having either a straight orlooped radiating antenna portion, etc.

One variation of an antenna cooling system may generally comprise acooling handle assembly with an elongate outer jacket extending from thehandle assembly and terminating at a tip which may be tapered. Amicrowave antenna may be positioned within the handle assembly and theouter jacket. An inflow tubing may extend into the handle body anddistally into at least a portion of the outer jacket. A correspondingoutflow tubing may also extend from within handle body such that thedistal ends of the inflow tubing and the outflow tubing are in fluidcommunication with one another. A fluid may be pumped into the handlebody via a pump through the inflow tubing such that the fluid comes intocontact directly along a portion of the length, or a majority of thelength, or the entire length of the antenna to allow for directconvective cooling of the antenna shaft. The fluid may exit the handlebody through the outflow tubing. Thus, the cooling assembly is effectivein cooling the antenna through direct contact rather than cooling thetissue surrounding the antenna, although the surrounding tissue may alsobe indirectly cooled through conduction via the assembly.

The cooling fluid used may vary depending upon desired cooling rates andthe desired tissue impedance matching properties. Various fluids may beused, e.g., liquids including, but not limited to, water, saline,Fluorinert®, liquid chlorodifluoromethane, etc. In other variations,gases (such as nitrous oxide, nitrogen, carbon dioxide, etc.) may alsobe utilized as the cooling fluid. In yet another variation, acombination of liquids and/or gases, as mentioned above, may be utilizedas the cooling medium.

The distal end of the microwave antenna may be optionally secured withinthe cooling jacket through various methods. For instance, the antennamay remain either electrically or mechanically unconnected to thecooling assembly tip or the two may be optionally joined via amechanical connection. In other variations, the antenna and tip may bemechanically and electrically connected, just electrically connected, orjust mechanically connected. Various mechanical fastening methods whichmay be utilized to mechanically connect the antenna and the tip mayinclude, e.g., adhesives, welding, soldering, clamping, crimping, etc.

Other cooling assembly variations may include an outer cooling jackethaving an inlet tube externally located from the lumen of the outerjacket. The inlet tube may be a separate tube member attached to thesurface of the outer jacket or it may be integrally formed with theouter jacket. Alternatively, an inlet lumen may be defined directlywithin the wall of the outer jacket. Yet another variation on antennacooling assembly may include a cooling jacket modified to cover only theradiating portion of the microwave antenna. The cooling jacket may thusbe configured to be shortened in length and may further omit a handleportion. Alternatively, another variation may have a cooling tube coiledaround at least a portion of the shaft.

Another alternative for cooling a microwave antenna may comprise apassively cooled balloon assembly typically comprising a microwaveantenna shaft or feedline with an inflatable balloon over a length ofthe shaft. The balloon member may be inflatable with a liquid or gas (orcombination of both) and attached along the microwave antenna shaftthrough any variety of attachment methods, e.g., adhesives, crimping,etc. Alternatively, a separate inflatable balloon may simply be placedover the antenna shaft and reside unattached to the microwave antenna.In use, the microwave antenna may be advanced percutaneously orlaparoscopically through the skin of a patient to position the antennaradiating portion within, near, or adjacent to a tumor. Once theradiating portion has been desirably positioned within the patient, theballoon may be inflated prior to or during microwave energy transmissionthrough the antenna. The inflation of the balloon may dilate the tissuesurrounding the shaft to urge the tissue out of contact with the shaftto prevent the tissue from overheating or becoming charred.

Alternative cooling methods and devices may also comprise passivecooling sheaths generally comprising a tubular cooling pack defining alumen into which the shaft of the antenna may be positioned. Anothervariation may comprise a conformable cooling sheath having a proximalhandle portion and a conformable portion which may be configured tospread over and cool the skin surface surrounding the area where theantenna shaft has been inserted.

Another alternative may comprise integrated cooling lumens definedthrough the length of the sheath. Optional barriers may be definedthrough the length of sheath to divide the interior lumen into at leasttwo separate volumes. Within these lumens, a first defined volume mayhold a first chemical or liquid (e.g., water, saline, etc.) and a seconddefined volume may hold a second chemical or liquid (ammonium chloride,sodium nitrate, or potassium chloride, etc.). When a cooling effect isdesired, the sheath may be flexed slightly such that the barriers arebroken or fractured within the sheath and allows for the mixing betweenthe chemicals to result in an endothermic reaction. Another alternativemay include a slidable sheath assembly comprising an inner tube, whichdefines a first volume for holding a first chemical or liquid, and aconcentric outer tube, which defines a second volume for holding asecond chemical or liquid. Alternative variations may have the coolingsheath or tube integrated with or within the microwave antenna shaft.

Cooling sheaths or jackets may be varied or tuned to match the requisitecooling for a given length of a microwave antenna. A typical microwaveantenna may generally be divided into at least three different regionsalong the length of its shaft. For instance, a microwave antenna may bedivided into a first region, second region, and third region.Accordingly, a multi-zone cooling assembly may be utilized to takeadvantage of optionally cooling multiple regions along the length of amicrowave antenna.

Finally, yet another variation may include a microwave antenna in whichthe diameters of the inner conductor are modified so that proximalportions of the inner conductor functions as a heat sink to facilitateconductive cooling of the microwave antenna. This may be accomplished bycreating an inner conductor having a larger proximal portion such thatthe proximal portion functions to draw and dissipate the heat at afaster rate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a microwave antenna assembly which may beutilized with the cooling systems described herein.

FIGS. 2A and 2B show representative cross-sectional end and side views,respectively, of a microwave antenna assembly which may be utilized withthe cooling systems described herein.

FIG. 3A shows a representative illustration of another variation of amicrowave antenna assembly which may be utilized with the coolingsystems described herein.

FIG. 3B shows a cross-sectional view of the antenna of FIG. 3A.

FIGS. 4A and 4B show a cross-sectional side view and an end view,respectively, of one variation of an antenna cooling system.

FIG. 4C shows a detail view from FIG. 4A of the cooling system handle.

FIGS. 4D and 4E show detail views from FIG. 4A of alternative coolingconfigurations for the antenna.

FIG. 5A shows a representative cross-sectional view of the distal end ofthe antenna within a cooling system.

FIGS. 5B to 5D show cross-sectional side views of alternativeattachments between the antenna and cooling system tip.

FIG. 5E shows a cross-sectional side view illustrating one variation inwhich the cooling system tip may be energized.

FIG. 6 shows a representative side view of another variation of thecooling system which may have an externally positioned fluid tube.

FIG. 7 shows a representative side view of yet another variation of thecooling system which may have an integrated fluid lumen defined within awall of the outer jacket.

FIG. 8 shows a side view of yet another variation of the cooling systemhaving a separate mandrel for structural support.

FIGS. 9A to 9C illustrate one variation in utilizing the device of FIG.8.

FIG. 10 shows yet another variation of a cooling system configured to beplaced over only the radiating portion of a microwave antenna.

FIG. 11 shows yet another variation of a cooling system comprising atube which may be coiled over the microwave antenna.

FIGS. 12A and 12B show side and cross-sectional views, respectively, ofa loop antenna variation configured to cool the antenna.

FIGS. 13A to 13C show end, cross-sectional side, and perspective views,respectively, of another variation of the system configured as a coolingsheath.

FIG. 14A shows a sheath in one variation used with a straight probemicrowave antenna.

FIG. 14B shows the sheath in another variation used with a looped probemicrowave antenna.

FIG. 14C shows the sheath in yet another variation used with a loopedprobe microwave antenna configured to cool the radiating looped antennaportion.

FIG. 15 shows a variation of a straight probe microwave antenna having adilating balloon used to push surrounding tissue away from the antennasurface.

FIG. 16 shows another variation of a straight probe microwave antennahaving multiple dilating balloons positioned along the length of theantenna.

FIG. 17 shows an exploded assembly view of another variation of thecooling system configured as a separate cooling sheath positionable overthe microwave antenna shaft.

FIG. 18 shows a side view of yet another variation of a cooling sheathconfigured to conform at least partially to the tissue surface.

FIGS. 19A and 19B show cross-sectional side and end views, respectively,of a cooling sheath.

FIGS. 20A and 20B show cross-sectional side and end views, respectively,of another variation on the cooling sheath having a divider which may bebreached to allow the intermixing of chemicals to create a coolingendothermic reaction.

FIGS. 21A and 21B show cross-sectional side views of yet anothervariation on the cooling sheath in which slidable concentric tubes haveopenings which are alignable to allow for the intermixing of chemicalsto create a cooling endothermic reaction.

FIG. 21C shows an end view of the cooling sheath of FIG. 21B where theopenings are aligned.

FIG. 22A shows a perspective view of one example of a cooling sheathpositioned over the microwave antenna.

FIGS. 22B and 22C show perspective views of other variations of coolingsheaths having a number of fluid lumens defined between the sheath andantenna surface.

FIG. 22D shows a perspective view of another variation in which thedielectric between the inner and outer conductors may define a number ofcooling lumens therethrough.

FIG. 23A shows a perspective view of a portion of a triaxial microwaveantenna shaft.

FIG. 23B shows an example of cooling lumens which may be defined throughthe dielectric between the outer conductor and the choke layer.

FIG. 24 shows a side view of a straight microwave antenna probedelineating the various regions along the antenna shaft which may be incontact with various regions of tissue.

FIG. 25 shows yet another variation of a cooling system which may beconfigured to delineate multiple regions of varied cooling along theshaft of the microwave antenna.

FIG. 26A shows yet another variation in which a diameter of the coaxialcable may be non-uniform such that a larger cable may have improvedpower handling capabilities which facilitate a decrease in thegeneration of high temperatures.

FIGS. 26B and 26C show cross-sectional side views of other transitionaldiameters for the inner conductor of FIG. 26A.

FIG. 27 shows a plot illustrating the temperature rise over time of anuncooled microwave antenna.

FIG. 28 shows a plot illustrating the decrease in microwave antennatemperature when the cooling system is activated.

DETAILED DESCRIPTION OF THE INVENTION

Various microwave antenna assemblies and cooling systems, as describedherein, are less traumatic than devices currently available and asdescribed in further detail below. Generally, in invasively treatingdiseased areas of tissue in a patient, trauma may be caused to thepatient resulting in pain and other complications. One cause of traumamay result from excess tissue being unnecessarily ablated by themicrowave antenna assembly. As the microwave antenna transmits microwaveenergy, the feedline or shaft of the antenna, as well as the radiationportion, may increase in temperature due to ohmic heating. Tissue incontact with a surface of the antenna may thus become charred or ablatedunnecessarily. Aside from unnecessary trauma, charred tissue maydecrease the effectiveness of the microwave antenna because of thechanging impedance of the tissue as it dries out and becomes charred.The cooling systems, as described herein, may be used in conjunctionwith various types of microwave antennas.

Examples of various types of microwave antenna assemblies which may beused with the cooling systems herein shall now be described. Forinstance, FIG. 1 shows a representative diagram of a variation of amicrowave antenna assembly 10 which may be used with a cooling system asdescribed herein. The antenna assembly 10 is generally comprised ofradiating portion 12 which may be connected by feedline 14 (or shaft)via cable 16 to connector 18, which may further connect the assembly 10to a power generating source 30, e.g., a generator. Assembly 10, asshown, is a dipole microwave antenna assembly, but other antennaassemblies, e.g., monopole or leaky wave antenna assemblies, may also beutilized. Distal portion 22 of radiating portion 12 preferably has atapered end 26 which terminates at a tip 28 to allow for insertion intotissue with minimal resistance. In those cases where the radiatingportion 12 is inserted into a pre-existing opening, tip 28 may berounded or flat.

Generally, the antenna assembly 10 in FIG. 1 shows a variation where acompressive load may be used to increase antenna strength. Proximalportion 24 is located proximally of distal portion 22, and junctionmember 20 is preferably located between both portions such that acompressive force is applied by distal and proximal portions 22, 24 uponjunction member 20. Placing distal and proximal portions 22, 24 in apre-stressed condition prior to insertion into tissue enables assembly10 to maintain a stiffness that is sufficient to allow for unaidedinsertion into the tissue while maintaining a minimal antenna diameter,as described in detail below.

Feedline 14 may electrically connect antenna assembly 10 via cable 16 togenerator 30 and usually comprises a coaxial cable made of a conductivemetal which may be semi-rigid or flexible. Feedline 14 may also have avariable length from a proximal end of radiating portion 12 to a distalend of cable 16 ranging between about 1 to 15 inches. Most feedlines maybe constructed of copper, gold, or other conductive metals with similarconductivity values, but feedline 14 is preferably made of stainlesssteel. The metals may also be plated with other materials, e.g., otherconductive materials, to improve their properties, e.g., to improveconductivity or decrease energy loss, etc. A feedline 14, such as onemade of stainless steel, preferably has an impedance of about 50Ω and toimprove its conductivity, the stainless steel may be coated with a layerof a conductive material such as copper or gold. Although stainlesssteel may not offer the same conductivity as other metals, it does offerstrength required to puncture tissue and/or skin.

FIGS. 2A and 2B show an end view and a cross-sectional view,respectively, of a conventional dipole microwave antenna assembly 40which may be utilized with the cooling systems described herein. Asseen, antenna assembly 40 has a proximal end 42 which may be connectedto a feedline 14 and terminates at distal end 44. The radiating portionof antenna 40 comprises proximal radiating portion 46 and distalradiating portion 48. Proximal radiating portion 46 may typically havean outer conductor 52 and an inner conductor 54, each of which extendsalong a longitudinal axis. Between the outer and inner conductors 52, 54is typically a dielectric material 56 which is also disposedlongitudinally between the conductors 52, 54 to electrically separatethem. A dielectric material may constitute any number of appropriatematerials, including air. Distal portion 58 is also made from aconductive material, as discussed below. Proximal and distal radiatingportions 46, 48 align at junction 50, which is typically made of adielectric material, e.g., adhesives, and are also supported by innerconductor 54 which runs through junction opening 60 and at leastpartially through distal portion 58. However, as discussed above, theconstruction of conventional antenna assembly 40 is structurally weak atjunction 50.

A further detailed discussion of microwave antennas which may beutilized herein may be found in U.S. patent application Ser. No.10/052,848 entitled “High-Strength Microwave Antenna Assemblies” filedNov. 2, 2001, now U.S. Pat. No. 6,878,147, and U.S. patent applicationSer. No. 10/272,058 entitled “High-Strength Microwave Antenna AssembliesAnd Methods Of Use” filed Oct. 15, 2002, now U.S. Pat. No. 7,128,739;each of which is incorporated herein by reference in its entirety.

An alternative microwave antenna having a curved microwave antenna mayalso be utilized with the cooling systems described herein as shown inFIG. 3A. Microwave antenna assembly 70 may comprise at least onemicrowave antenna 72 electrically connected to generator 82. Microwaveantenna 72 preferably comprises shaft or feedline 74 with a distal endfrom which antenna or inner conductor 76 extends to define the ablationregion 90. The proximal end of feedline 74 preferably comprises coupler78 which electrically couples the antenna 72 to generator 82 via powertransmission cable 80. The cable 80 is preferably a flexible cable whichallows for the positioning of antenna 72 relative to a patient.

Feedline 74 is preferably a coaxial cable, as shown by the cross-section3B-3B in FIG. 3B taken from FIG. 3A. The feedline 74, similar tofeedline 14 described above, may be formed of outer conductor 84surrounding inner conductor 86. Conductors 84, 86 may be made of aconductive metal which may be semi-rigid or flexible. Most feedlines 84,as described above, may be constructed of metals such as stainlesssteel. Alternatively, metals such as copper, gold, or other conductivemetals with similar conductivity values may also be utilized. Adielectric material 88 is preferably disposed between outer and innerconductors 84, 86, respectively, to provide insulation therebetween andmay be comprised of any appropriate variety of conventional dielectricmaterials.

Additional details regarding the curved loop microwave antennaconfiguration which may be utilized herein are further described in U.S.patent application Ser. No. 10/272,314 entitled “Microwave AntennaHaving A Curved Configuration” filed Oct. 15, 2002, now U.S. Pat. No.7,197,363, which is incorporated herein by reference in its entirety.

FIGS. 4A and 4B show a cross-sectional side view and an end view,respectively, of one variation of an antenna cooling system which may beutilized with any number of conventional microwave antennas or themicrowave antennas described herein, particularly the straight probeconfiguration as shown in FIGS. 1 and 2A-2B. Although this variationillustrates the cooling of a straight probe antenna, a curved or loopedmicrowave antenna may also utilize much of the same or similarprinciples, as further described below. Antenna cooling assembly 100 maygenerally comprise a cooling handle assembly 102 and an elongate outerjacket 108 extending from handle assembly 102. Outer jacket 108 mayextend and terminate at tip 110, which may be tapered to a sharpenedpoint to facilitate insertion into and manipulation within tissue, ifnecessary. Microwave antenna 104 may be positioned within handleassembly 102 such that the radiating portion 106 of antenna 104 extendsdistally into outer jacket 108 towards tip 110. Inflow tubing 114 mayextend into a proximal end of handle body 112 and distally into aportion of outer jacket 108. Outflow tubing 116 may also extend fromwithin handle body 112 such that the distal ends of inflow tubing 114and outflow tubing 116 are in fluid communication with one another, asdescribed in further detail below.

FIG. 4C shows handle assembly detail 118 from FIG. 4A. As shown, handlebody 112 may be comprised of proximal handle hub 122, which encloses aproximal end of antenna 104, and distal handle hub 124, which may extenddistally into outer jacket 108. Proximal handle hub 122 and distalhandle hub 124 may each be configured to physically interfit with oneanother at hub interface 130 to preferably form a fluid tight seal.Accordingly, proximal handle hub 122 may be configured to be receivedand secured within a correspondingly configured distal handle hub 124,seen in the figure as a male-female connection. Proximal and distalhandle hubs 122, 124 may each be formed from the same (or similar) ordifferent materials. If hubs 122, 124 are fabricated from the samematerial, a variety of non-conductive materials are preferably utilized,e.g., polymers, polyimides, plastics, etc. Alternatively, proximalhandle hub 122 may be fabricated from a metal or alloy, e.g., stainlesssteel, platinum, nickel, nickel-titanium, etc., while distal handle hub124 (or just the handle portion over the radiating portion of themicrowave antenna) may be fabricated from one of the non-conductivematerials previously mentioned.

The distal ends of inflow tubing 114 and outflow tubing 116 may bepositioned within handle body 112 such that fluid may be pumped intohandle body 112 via a pump (not shown) through inflow tubing 114. Fluidentering handle body 112 may come into direct contact with at least aportion of the shaft of antenna 104 to allow for convective cooling ofthe antenna shaft to occur. The fluid may be allowed to exit handle body112 via outflow tubing 116. An additional inlet tube 126 may bepositioned within antenna cooling assembly 100 to extend between handlebody 112 and radiating portion 106 of antenna 104 and a correspondingoutlet tube 128 may also extend between handle body 112 and radiatingportion 106. The proximal end of inlet tube 126 may be in fluidcommunication with inflow tubing 114 to allow the cooling fluid to flowdistally within outer jacket 108 towards antenna radiation portion 106.Alternatively, inlet tube 126 and outlet tube 128 may be omitted fromcooling assembly 100 and outer jacket 108 may remain in direct fluidcommunication with inflow tubing 114 and outflow tubing 116 such thatfluid contacts the antenna 104 directly along a portion of the length,or a majority of the length, or the entire length of antenna 104. Thus,the cooling assembly 100 is effective in cooling the antenna 104directly rather than cooling the tissue surrounding the antenna 104,although the surrounding tissue may also be conductively cooled viaassembly 100.

FIGS. 4D and 4E shows outer jacket detail variations 120, 120′,respectively, from FIG. 4A FIG. 4D shows one variation where the distalend 132 of inlet tube 126 may extend distally through outer jacket 108.The opening at distal end 132 may be positioned within outer jacket 108near or at the distal end of outer jacket 108 such that distal end 132opens to fluid channel 134. The cooling fluid may enter fluid channel134 and fill the volume surrounding at least a portion of the antenna104, and preferably surrounding at least the radiation portion 106. Asfluid enters fluid channel 134, it may be withdrawn through a distalopening in outlet tube 128, which is preferably located proximally ofdistal end 132 to allow for increased convective cooling between thecooling fluid and the antenna 104. Alternatively, each of the distalends of inlet tube 126 and outlet tube 128 may be aligned with oneanother. In either case, the cooling fluid may directly contact theouter surface of the antenna 104 and envelope the antenna 104 ratherthan being in conductive contact through some additional thermalinterface. Allowing the direct fluid-to-antenna contact enables directconvective cooling to occur and may thereby facilitate the heat transferfrom the antenna to the cooling fluid.

The cooling fluid may be pumped using positive pressure through inlettube 126; alternatively, negative pressure may also be used to draw thefluid out of the region through outlet tube 128. Negative pressurethrough outlet tube 128 may be utilized either alone or in conjunctionwith positive pressure through inlet tube 126. Alternatively, positivepressure through inlet tube 126 may be utilized either alone or inconjunction with negative pressure through outlet tube 128. In pumpingthe cooling fluid through cooling assembly 100, the cooling fluid may bepassed through assembly 100 at a constant and uniform flow rate. Inanother variation, the flow may be intermittent such that a volume ofcooling fluid may be pumped into fluid channel 134 and allowed to warmup by absorbing heat from the antenna. Once the temperature of the fluidreaches a predetermined level below temperatures where thermal damage totissue occurs, e.g., about 43° to 45° C., the warmed fluid may beremoved and displaced by additional cooling fluids. Temperature sensors(such as thermistors, thermocouples, etc.) may be incorporated within orupon the outer jacket 108 to sense the fluid and/or outer jacket 108temperatures. The system may be configured to automatically pumpadditional cooling fluid into cooling assembly 100 once the sensedtemperature reaches the predetermined level or it may be configured tonotify the user via, e.g., an audible or visual alarm.

The cooling fluid used may vary depending upon desired cooling rates andthe desired tissue impedance matching properties. Preferably,biocompatible fluids having sufficient specific heat values forabsorbing heat generated by microwave ablation antennas may be utilized,e.g., liquids including, but not limited to, water, saline, Fluorinert®,liquid chlorodifluoromethane, etc. In another variation, gases (such asnitrous oxide, nitrogen, carbon dioxide, etc.) may also be utilized asthe cooling fluid. For instance, an aperture may be configured at theopening of distal end 132 to take advantage of the cooling effects fromthe Joule-Thompson effect, in which case a gas, e.g., nitrous oxide, maybe passed through the aperture to expand and cool the enclosed antenna104. In yet another variation, a combination of liquids and/or gases, asmentioned above, may be utilized as the cooling medium.

FIG. 4E shows another variation in detail 120′ within outer jacket 108which incorporates a barrier or gasket 138 to separate the radiatingportion 142 of antenna 106 from a proximal portion of the antenna shaft.Barrier 138 may be, e.g., a polymeric or rubber material, configured tofunction as a gasket to maintain a fluid tight seal around the shaft ofthe antenna 106. Fluid channel 140 may be defined within outer jacket108 distally of barrier 138 within which radiating portion 142 may bepositioned. A fluid, such as any one of the fluids mentioned above, maybe maintained statically within fluid channel 140 to absorb heatgenerated by radiating portion 142. Alternatively, channel 140 may befilled with a fluid, high-temperature chemical, e.g., epoxy, for betterimpedance matching with the antenna 106. A separate fluid channel may bedefined proximally of barrier 138 surrounding the remaining shaftportion of the antenna. An inlet tube 136 may be positioned within thisproximal channel to allow for the exchange of cooling fluids therewithinin a manner as described above such that the fluid is allowed todirectly contact the antenna shaft surface.

The distal end of the microwave antenna may optionally be secured withinthe cooling jacket through a variety of methods. FIG. 5A shows anillustrative cross-sectional view of cooling assembly distal end 150which shows microwave antenna 154 positioned within outer jacket 152.Although antenna 154 may remain either electrically or mechanicallyunconnected to cooling assembly tip 156, the two may optionally bejoined via a connection 158. FIG. 5B shows one variation of connectingantenna 154 to tip 156 in which they may be mechanically andelectrically connected. Tip 156 may be fabricated from a metal or alloy,e.g., stainless steel, and define a contact channel at its proximal endfor receiving antenna 160, which may also be metallic. Antenna end 160may be secured into an electrically conductive connection 162 with tip156 through various mechanical fastening methods, e.g., adhesives,welding, soldering, clamping, crimping, press-fit, etc., such thatconnection 162 is a mechanical joint sufficiently strong enough toresist failure when deployed into tissue while also providing for anelectrical connection.

FIG. 5C shows another variation where antenna 164 may be mechanicallyconnected to but electrically insulated from tip 156. Antenna 164, or atleast the portion of antenna 164 in contact with tip 156, may have aninsulative layer 166 over its outer surface. Thus, tip 156 may remainelectrically insulated from antenna 164 yet retain the structuralconnection therebetween, as described above. In yet another alternative,FIG. 5D shows a connection in which antenna 154 may be electricallyconnected to tip 156 via a wire or cable 168. Such a connection may beused to provide for electrical communication between antenna 154 and tip156 but does not provide for structural support between the two.

In the case where antenna 164 is structurally attached to tip 156 yetelectrically insulated, as shown in FIG. 5C, FIG. 5E shows a variationwhere electrical communication with tip 156 may be maintained with anexternally located power source 161 to provide power for energizing tip156. Energized tip assembly 151 shows antenna 164 structurally connectedto tip 156 with insulative layer 166 positioned therebetween. Antenna164 is shown positioned within outer jacket 153. Rather than having adirect electrical connection between wire 159 and tip 156, wire 159 maybe connected to choke 155 such that power source 161 is electricallyconnected to tip 156 through choke 155, in an alternative variation. Inyet another variation, power source 161 may instead be electricallyconnected to tip 156 via outer conductor 157 through wire 159. In thevariations where wire 159 is connected to either choke 155 or outerconductor 157, an electrical connection between antenna 164 and tip 156is present.

Rather than utilizing separate inlet and outlet tubes, other variationsmay also be utilized. FIG. 6 shows a side view of another coolingassembly variation 170. In this variation, outer jacket 172 may have aninlet tube 176 externally located from the lumen of outer jacket 172.Tube 176 may be fabricated from the same or similar material as outerjacket 172, as described above, or it may be made from a materialdifferent from outer jacket 172, provided that it is preferablynon-electrically conductive. Tube 176 may be a completely separate tubemember attached to the surface of outer jacket 172. Alternatively, tube176 may be integrally formed with outer jacket 172. In either case,cooling fluid may be pumped through tube 176 to flow distally alongouter jacket 172, as shown by the arrows, until it passes throughopening 180, which may allow for the fluid communication between tube176 and outlet channel 178 defined through the interior of outer jacket172. Opening 180 may be defined between tube 176 and outlet channel 178at a predetermined location along outer jacket 172 proximal to tip 174.The location of opening 180 may depend upon the desired cooling effectsand the desired location along the antenna over which the cooling fluidmay flow. In another variation, the cooling fluid may be pumped intocooling jacket 172 through outlet channel 178 and the discharged fluidmay be returned through tube 176.

FIG. 7 shows a side view of another cooling assembly variation 190.Outer jacket 192 may be seen with tip 194 at its terminal end. In thisvariation, however, inlet lumen 196 may be defined directly within thewall of outer jacket 192. Inlet lumen 196 may terminate at opening 200which may be in fluid communication with outlet channel 198, withinwhich a microwave antenna may be situated. Although opening 200 is shownterminating at the distal end of outer jacket 192, opening 200 may bedefined at some predetermined location along outer jacket 192 proximalto tip 194 between inlet lumen 196 and outlet channel 198. Furthermore,outer jacket 192 may be fabricated out of any one of the materials asdescribed above.

A combination introducer and cooling sheath is shown in the side view ofassembly 210 in FIG. 8. Cooling introducer assembly 210 may comprise apolymeric tubing 212 having tubing hub 214 located at the proximal endof tubing 212. Tip 216, which may be tapered to facilitate assembly 210introduction into tissue, may be located at the distal end of tubing212. A removable elongate mandrel 218 may be inserted within tubing 212to provide structural support and column strength to tubing 212 duringinsertion of assembly 210 into tissue. Mandrel 218 may be fabricatedfrom various materials having sufficient strength to withstand bendingmoments generated by tubing 212 during tissue insertion, e.g., stainlesssteel, and may be configured to slidably fit within lumen 220.

FIGS. 9A to 9C show one example of how assembly 210 may be used as anintroducer and cooling jacket for the ablative treatment of tissue.Tubing 212, with mandrel 218 positioned within, may be inserted into thetissue of a patient 230 until a distal portion of tubing 212 ispositioned adjacent to or within a diseased region of tissue, e.g.,tumor 232, as shown in FIG. 9A. Once tubing 212 has been desirablypositioned, inner mandrel 218 may be removed from tubing 212 whilemaintaining the position and orientation of tubing 212 within patient230, as shown in FIG. 9B. Microwave antenna 236 may then be insertedwithin lumen 220 of tubing 212 and advanced distally therewithin suchthat radiating portion 238 of antenna 236 is positioned within thedistal portion of tubing 212 which is adjacent to or within tumor 232.The proximal end of antenna 236 may have cooling hub 234 connectedthereto and cable 240 extending proximally for connection to a microwaveand/or RF power supply (not shown).

The length of antenna 236 may be configured to fit within tubing 212such that tubing hub 214 and cooling hub 234 may come into contact withone another and locked together, as shown in FIG. 9C. One or both hubs214, 234 may be configured to releasably lock together through anymethod of mechanical attachment. For example, hubs 214, 234 may bethreaded to screw onto one another, or hubs 214, 234 may be configuredto be secured via an interference fit, or any other mechanical fasteningmethod known in the art may be utilized. Furthermore, a gasket may beprovided to fit in-between hubs 214, 234 to provide for a fluid-tightseal therebetween. Cooling hub 234 may be fluidly connected to a pumpvia inlet tube 242 and outlet tube 244. Once hubs 214, 234 have beensecured together, cooling fluid may be introduced through inlet tube 242and through hub 234 such that the fluid enters into lumen 220 toenvelope and contact antenna 236 to cool antenna 236, if desired. Thefluid may be removed from lumen 220 via outlet tube 244, which may alsobe in fluid communication with lumen 220 via hub 234. Once the procedurehas been completed, the entire assembly may be removed from the tissue.

Yet another variation on antenna cooling assembly 250 may be seen in theside view in FIG. 10. In assembly 250, cooling jacket 256 may bemodified to cover only the radiating portion 254 of the microwaveantenna. Cooling jacket 256 may thus be configured to be shortened inlength from, e.g., cooling jacket 108 described above, and may furtheromit a handle portion to form cooling channel 262 around radiatingportion 254. Inlet tube 258 and outlet tube 260 may be incorporated withjacket 256 to provide the cooling fluid flow within cooling jacket 256.The remainder of antenna shaft 252 may remain uncovered by coolingjacket 256.

FIG. 11 shows another variation in cooling assembly 270 in which antennashaft 272 may have cooling tube 276 coiled around at least a portion ofshaft 272. Cooling tube 276 may have cooling fluid flowing therethroughvia inlet tube 278 and outlet tube 280 connected to a pump. In thevariation shown, tube 276 is coiled around a portion of antenna shaft272 up to radiating portion 274. In an alternative variation, tube 276may also be coiled around radiating portion 274, in which case tube 276,or the portion of tube 276 covering radiating portion 274, is preferablyfabricated from a polymeric or plastic material. Furthermore, tube 276may be coiled only over radiating portion 274. An optional covering orsheath, preferably made from a polymeric material, e.g., PTFE, Pebax®,etc., may be formed or fitted over the coiled tube 276 (or a portion ofthe coiled tube 276) to provide a lubricious surface for assembly 270for insertion into tissue.

Another variation on the cooling assembly is shown in FIGS. 12A and 12B,which show side and cross-sectional views, respectively, of a loopantenna variation 290 configured to cool the antenna. This variation isshown for a microwave antenna having a looped antenna, but theprinciples are applicable to straight antenna probes, as will bedescribed in further detail below. In assembly variation 290, antennashaft 292 may have fluid outer tube 294 positioned within antenna shaft292 and fluid inner tube 296 coaxially positioned within outer tube 294.The assembly of tubes 294, 296 may form inner conductor assembly 298 andeach tube may extend through the length of antenna shaft 292 and beyondto form the curved antenna portion. The distal end of fluid inner tube296 may terminate proximally of the distal end of fluid outer tube 294,which is preferably enclosed at its terminal end. The distal end offluid inner tube 296 may also define an opening to allow for fluidcommunication between tubes 294, 296.

Fluid inner tube 296 may define an inflow lumen 300, as shown in FIG.12B, and fluid outer tube 294 may define an outflow lumen 302 in thespace between tubes 294, 296. Thus, cooling fluid may be circulatedthrough the inner conductor 298 itself to cool the antenna duringmicrowave energy transmission. Tubes 294, 296 may be formed from anelectrically conductive material suitable for microwave transmission,e.g., stainless steel, platinum, gold, nickel, etc., or stainless steelplated with an electrically conductive material having a lowerelectrical resistivity than the stainless steel.

Aside from utilizing direct contact between the cooling fluid and themicrowave antenna, other variations may employ cooling sheaths, such asthe variation shown in FIGS. 13A to 13C, which show end, cross-sectionalside, and perspective views, respectively, of cooling sheath assembly310. Sheath assembly 310 may generally comprise main tubular member 312which defines an antenna lumen 316 therethrough. Tubular member 312 maybe fabricated of a polymeric or plastic material, as described above,and preferably defines a diameter sufficient to accommodate the shaft ofa microwave antenna positioned within antenna lumen 316. Furthermore,tubular member 312 may be at least partially formed of a metallicmaterial (preferably proximal to the radiating portion), or member 312may be formed of a ceramic material. Tubular member 312 is preferablywide enough to allow for direct contact or close contact against anouter surface of the microwave antenna when the antenna is positionedwithin to facilitate the heat transfer. The tubular member 312 may alsobe formed of a material, e.g., heat-shrink polymers, which allow fortubular member 312 to conform to an outer surface of the microwaveantenna to ensure close thermal contact. Alternatively, a thermallyconductive and conformable material, such as a gel or fluid, may bepoured or placed within the space, if present, between antenna lumen 316and the inner wall of tubular member 312 to ensure consistent thermalcontact between the two.

A coaxially positioned fluid tube 314, as seen in FIG. 13A, may bepositioned around tubular member 312 and define fluid channel 322, asseen in the cross-sectional view of FIG. 13B. Fluid tube 314 may beformed as a common channel such that fluid contained therewithinenvelopes or encompasses the outer surface of tubular member 312. Fluidtube 314 may also be varied in length to surround a majority of tubularmember 312 or just a portion of it depending upon the desired coolingeffects. Inlet tube 318 may be positioned within fluid channel 322 suchthat the distal end of inlet tube 318 is positioned near or at thedistal end of fluid tube 314 while the distal end of outlet tube 320 maybe positioned near or at the proximal end of fluid tube 314 tofacilitate the heat transfer. Fluid tube 314 may be integrallyfabricated with tubular member 312; however, fluid tube 314 may also bemade of a material different from tubular member 312 and attachedthrough one of any mechanical fastening methods. The distal end of fluidtube 314 and the distal end of tubular member 312 may be joinedtogether; and the proximal end of fluid tube 314 may be attached,connected, or integrally formed with either the proximal end of tubularmember 312 or at a predetermined location along an outer surface distalof the proximal end of tubular member 312. Thus, fluid channel 322 maybe formed as a common circumferential fluid channel. If cooling sheathassembly 310 is positioned over only the shaft portion of a microwaveantenna, assembly 310 may be made from a metallic material such asstainless steel. Alternatively, if assembly 310 is also configured to bepositioned over the radiating portion of an antenna, the entire assembly310, or at least the portion of the assembly 310 covering the antenna,is preferably made from a polymeric or plastic material, as describedabove. The distal end of assembly 310 may be formed into a tapered oratraumatic end 324 to prevent damage to surrounding tissue when assembly310 is inserted into a patient.

FIG. 14A shows a side view of a cooling sheath assembly in one variation330 used with a straight probe microwave antenna. As shown in thisvariation, assembly 330 may comprise cooling sheath 332 for placementover a length of antenna shaft 344. The radiating portion 342 isuncovered in this variation, although alternative sheath designs may beemployed to entirely cover the radiating portion 342 as well. Assembly330 may also comprise hub 334, through which inlet tube 338 and outlettube 340 may be in fluid communication with sheath 332 to allow forcirculation of the cooling fluid. An optional adjustable seeming member,e.g., tightening knob 336, may be provided on hub 334, or directly onsheath 332, to prevent sheath 332 from moving relative to antenna shaft344 by tightening knob 334 in a direction of the arrow shown. Knob 336may be untightened as well to allow for removal or adjustment of sheath332 over the antenna. Tightening knob 336 is shown as a rotatablesecuring mechanism, e.g., a tightening screw, however, other tighteningmethods as known in the art may be employed for securing sheath 332 toantenna shaft 344.

FIG. 14B shows a side view of the cooling sheath assembly of FIG. 14A inanother variation 350 in which sheath 332 may be placed over the shaft356 of a microwave antenna having a looped radiating portion 354. Invariation 350, sheath 332 may be positioned over shaft 356 such that theportion of shaft 356 up to its distal end 352 is covered. Radiatingportion 354 may remain uncovered in this variation. FIG. 14C shows thecooling sheath assembly in yet another variation 360 used with a loopedmicrowave antenna configured to cool the radiating looped antennaportion. In this variation, sheath 332 may be used with a loopedmicrowave antenna having an inner conductor configured to have coolinglumens integrated within, as shown and described for FIGS. 12A and 12Babove. Alternatively, and as shown in FIG. 14C, a separate coolingballoon or sheath 362 may be formed to surround the radiating portion354.

Balloon or sheath 362 is described in further detail in U.S. Pat. No.7,197,363, which has been incorporated herein above. Generally, balloonor sheath 362 may be disposed over the curved radiating portion 354 ofthe microwave antenna. Balloon or sheath 362 may be in a deflated stateduring the deployment of the antenna through sheath 332 and/or withinthe tissue, but once the curved antenna 354 has been desirablypositioned, balloon 362 may be filled with the cooling fluid, e.g.,chilled saline, water, etc., until it has sufficiently inflated. Thesize of balloon 362 may be varied according to the desired radiativeeffects (for impedance matching purposes), the length of radiatingportion 354, as well as the type of tissue which the antenna is insertedwithin. Furthermore, the cooling fluid may be maintained staticallywithin balloon 362 or it may be circulated in a manner as describedabove.

Another alternative for cooling a microwave antenna and/or preventingunnecessary tissue damage by a heated antenna feedline or shaft is seenin FIG. 15. The variation shown is a passively cooled balloon assembly370 which may typically comprise microwave antenna shaft or feedline 372with an inflatable balloon 374 positioned over a length of shaft 372.FIG. 15 shows balloon 374 in an inflated configuration over themicrowave antenna. A balloon member 374, which may be inflatable with aliquid or gas (or combination of both) such as saline, water, air,nitrogen, etc., may be attached along microwave antenna shaft 372 atproximal attachment region 376 and distal attachment region 378 throughany variety of attachment methods, e.g., adhesives, crimping, etc.Alternatively, a separate inflatable balloon may simply be placed overantenna shaft 372 and reside unattached to the microwave antenna.Balloon 374 may reside along shaft 372 to cover the portion of the shaft372 which may come into contact with tissue when inserted into apatient. Distal attachment region 378 may be positioned proximally ofantenna radiating portion 380 such that the entire radiating portion 380is not covered by balloon 374. Alternatively, distal attachment region378 may be positioned near or at the distal tip of the antenna so that aportion, or a majority of radiating portion 380, is at least partiallycovered by balloon 374.

In use, the microwave antenna may be advanced percutaneously orlaparoscopically through the skin 382 of a patient to position antennaradiating portion 380 near or adjacent to tumor 384. Balloon 374 ispreferably in a deflated configuration during the insertion through theskin 382, although balloon 374 may alternatively be inflated prior to orduring insertion through skin 382, depending upon the circumstances.Once radiating portion 380 has been desirably positioned within thepatient, balloon 374 may be inflated via an inlet tube prior to orduring microwave energy transmission through the antenna. The inflationof balloon 374 may dilate the tissue 386 surrounding the shaft 372 andurge the tissue 386 out of contact with shaft 372. The radiating portion380 may remain in direct contact with tumor 384 to effect microwaveablation treatment. Having balloon 374 move tissue 386 away from directcontact with antenna shaft 372 helps to prevent the tissue 386 fromoverheating or becoming ablated.

An alternative multi-balloon assembly 390 is shown in the side view ofFIG. 16. The microwave antenna assembly 390 may be divided into several,i.e., two or more, regions along its shaft. For instance, first antennaregion 392, second antenna region 394, and third antenna region 396 mayeach have a respective first balloon 400, second balloon 402, and thirdballoon 404 over each region such that each balloon 400, 402, 404 isadjacent to one another along the shaft outer surface. Each balloon 400,402, 404 may be attached to the microwave antenna distal of connectorhub 414 at first, second, third, and fourth attachment regions 406, 408,410, 412, respectively, through one of any attachment methods asdescribed above. A balloon may be positioned over radiating portion 398or radiating portion 398 may be left exposed, as shown in the figure.The number of balloons in this example are merely illustrative and feweror greater number of balloons may be utilized depending upon the desiredconfiguration and cooling results. Moreover, each balloon 400, 402, 404may be in fluid communication with one another in series such that allthe balloons 400, 402, 404 may be inflated simultaneously.Alternatively, each balloon 400, 402, 404 may be individually inflatablesuch that a single balloon, or a combination of balloons, may beinflated while the other balloons may remain un-inflated, depending uponthe desired cooling results. Moreover, each balloon may be inflatablewith a liquid or gas (or combination of both) such as saline, water,air, nitrogen, etc., as described above. Furthermore, although astraight microwave antenna probe is shown in the figures, this isintended to be illustrative; alternatively, a microwave antenna having acurved radiating portion may also be utilized.

Aside from the use of inflatable balloons, alternative cooling methodsand devices may comprise passive cooling sheaths, as shown in theexploded assembly 420 of FIG. 17. Assembly 420 may comprise a microwaveantenna 422 having a radiating portion 424; in this example, a curvedradiating portion 424. A tubular cooling pack 426 may define a lumen 428into which the shaft of antenna 422 may be positioned. Both antenna 422and cooling pack 426 may be positioned within a handle lumen 434 definedwithin handle 430. An optional insulation layer 432, e.g., foam, rubber,etc., may be disposed upon the inner surface of handle lumen 434 betweencooling pack 426 and handle 430. Cooling pack 426 may simply be aplastic or polymeric tubular container of chilled or frozen water orsaline, or another fluid which is preferably biocompatible, which may becooled prior to use with the microwave antenna. Alternatively, coolingpack 426 may contain gels or chemicals which may be mixed (e.g., amixture of water, urea, and ammonium chloride; alternatively, a mixtureof potassium chloride or sodium nitrate and water, etc.) such that anendothermic reaction results and cooling of the antenna 422 may beachieved. Moreover, cooling pack 426 may be configured to come intointimate contact with the shaft of antenna 422 to ensure good thermalcontact. Handle 430 may be molded from various materials, e.g.,polymers, plastics, etc., and it may be configured as a simple tubularhandle. Alternatively, it may be ergonomically molded to allow forbetter handling by the user. The handle lumen 434 is preferably justwide enough to allow for the insertion of cooling pack 426 so thatthermal contact between the two may occur. The cooling assembly 420 maybe assembled prior to use with the antenna 422 such that the entireassembly is inserted into the tissue altogether; alternatively, it maybe assembled within the tissue during tissue ablation.

Another variation may be seen in the side view of conformable coolingsheath assembly 440 in FIG. 18. The antenna shaft or feedline 442 of amicrowave antenna may be inserted through a handle lumen 450 definedthrough conformable cooling sheath 440. Cooling sheath 440 may comprisea proximal handle portion 444 and a conformable portion 446 which may beconfigured to spread over and cool the skin surface 452 surrounding thearea where the antenna shaft 442 has been inserted. Proximal handleportion 444 may be comprised of a polymeric or plastic material whichmay be adapted to maintain its configuration while conformable portion446 may be comprised of a polymeric material adapted to spread out andconform against skin surface 452 over contact surface 448. Conformablesheath assembly 440 may be filled with any one of the liquids, gases,and/or chemical mixtures as described above.

Alternative cooling sheaths are further shown in FIGS. 20A to 21C. Across-sectional side and end view of cooling sheath 460 is shown inFIGS. 19A and 19B, respectively, for comparison purposes. As shown, asimple cooling sheath 460, as described above, may define antenna lumen462 therethrough. FIGS. 20A and 20B show cross-sectional side and endviews of cooling sheath 470. Antenna lumen 474 may be defined throughthe length of sheath 470. Barriers 472 may be defined through the lengthof sheath 470 to divide the interior lumen into at least two separatevolumes. A first defined volume 476 may hold a first chemical or liquid(e.g., water, saline, etc.) and second defined volume 478 may hold asecond chemical or liquid (ammonium chloride, sodium nitrate, orpotassium chloride, etc.). When a cooling effect is desired, sheath 470may be flexed slightly such that barriers 472 may be broken or fracturedwithin sheath 470 to allow for the mixing between the chemicals fromfirst volume 476 and second volume 478 to result in an endothermicreaction.

Another alternative may be seen in the cross-sectional side views ofFIGS. 21A and 21B and the end view of FIG. 21C of slidable sheathassembly 480. As shown in FIG. 21A, sheath assembly 480 may comprise aninner tube 484, which defines a first volume 492 for holding a firstchemical or liquid, and a concentric outer tube 482, which defines asecond volume 494 for holding a second chemical or liquid. Thecomposition of the first chemical and/or second chemical contained intheir respective volumes may include any of the chemicals and/or liquidsmentioned above. Outer tube 482 may define a plurality of openings 488over its inner surface and inner tube 484 may also define a plurality ofopenings 490 over its outer surface. Openings 488, 490 may be defined ineach of their respective tubes such that when inner tube 484 and outertube 482 are in a first misaligned configuration relative to oneanother, their respective openings are blocked, as shown in FIG. 21A.However, inner tube 484 and outer tube 482 may be moved longitudinallyand/or rotationally relative to one another into a second alignedconfiguration such that openings 488, 490 may be aligned with oneanother and allow for the mixing of the respective chemicals to producea cooling effect within antenna lumen 486, as shown in FIGS. 21B and21C. These variations are intended to be illustrative and any variationson the number of openings or the manner in which openings may be alignedto allow for the mixture of various chemicals or liquids are intended tobe within the scope of the invention.

Alternative variations in which the cooling sheath or tube may beintegrated with or within the microwave antenna shaft are shown in thefollowing FIGS. 22A to 22D. FIG. 22A shows a perspective view of aportion of a microwave antenna shaft assembly 500 in which outer tubing508 may be formed as an integral part of the microwave antenna. Theantenna is shown as comprising, in part, outer conductor 502 coaxiallysurrounding inner conductor 504 with dielectric 506 disposedtherebetween. Outer tubing 508, which may be comprised of a metallic,e.g., stainless steel, or polymeric material, as described above, maysurround the length, or at least a partial length of the microwaveantenna. Outer tubing 508 may define a cooling lumen 510 between theouter conductor 502 through which a cooling fluid may be pumped throughor simply filled.

FIG. 22B shows another cooling tube variation 520 in which outer tubing522 may surround the microwave antenna, as in assembly 500 of FIG. 22A.Tubing 522, however, may include a barrier or divider 524 whichseparates the cooling lumen into at least a first lumen 526 and a secondlumen 528, which may act as inlet and outlet lumens, respectively, for acooling fluid to be flowed through. Divider 524 may be formed of thesame or similar material as outer conductor 502 and/or outer tubing 522.FIG. 22C shows yet another variation 530 in which outer tube 532 maycomprise a number of longitudinally formed dividers 534, 536, 538, 540,and 542 to create a number of corresponding cooling lumens 544, 546,548, 550, and 552 in the space between outer conductor 502 and outertubing 532. The cooling lumens may be utilized as inlet lumens or outletlumens or various combinations thereof depending upon the desiredcooling results. The number of dividers and cooling lumens is intendedmerely to be illustrative of the various combinations and numbers ofcooling lumens which may be formed.

FIG. 22D shows yet another variation 560 in which cooling lumens may beformed within the space between outer conductor 502 and inner conductor504, where a dielectric material is typically located. In thisvariation, longitudinally defined dividers 564, 566, 568, 570, and 572may be formed of an electrically non-conductive material, e.g.,polymers, to divide the space into a number of corresponding coolinglumens 574, 576, 578, 580, and 582. An optional cooling tube 562 may beutilized and positioned over outer conductor 502. As above, the coolinglumens may be utilized as inlet lumens or outlet lumens or variouscombinations thereof depending upon the desired cooling results.Moreover, the number of dividers and cooling lumens is intended merelyto be illustrative and not limiting in scope.

In certain variations of the microwave antenna, an electrical choke maybe utilized to improve the energy focus of an antenna assembly. Theelectrical choke and its use is described in further detail in U.S. Pat.Nos. 6,878,147 and 7,128,739, which have been incorporated herein byreference above. Generally, the choke may be disposed on the antennaproximally of the radiating section. The choke is preferably placed overa dielectric material which may be disposed over the antenna. The chokeis preferably a conductive layer and may be further covered by a tubingor coating. A cross-sectional view of a triaxial antenna 590 may be seenin FIG. 23A having inner conductor 592 and outer conductor 594 withdielectric 596 disposed therebetween. The choke layer 598 may be seenformed over outer conductor 594 with dielectric 600 disposed between thetwo layers. FIG. 23B shows a cooling choke variation 610 in which anumber of longitudinally defined dividers 612, 614, 616, 618, and 620may form a number of corresponding cooling lumens 622, 624, 626, 628,and 630. The dividers may be formed of an electrically non-conductivematerial, e.g., polymers, and the cooling lumens may be utilized asinlet lumens or outlet lumens or various combinations thereof dependingupon the desired cooling results.

Cooling sheaths or jackets, as described above, may be varied or tunedto match the requisite cooling for a given length of a microwaveantenna. A typical microwave antenna may generally be divided into atleast three different regions along the length of its shaft. Forinstance, in FIG. 24, a side view of microwave antenna 640 may be seendivided into a first region 642, second region 644, and third region646. First region 642 may generally comprise the radiating antenna orthe region of active heating during microwave ablation. It may bedesirable to cool this region 642 to maintain optimal energy delivery bypreventing the surrounding tissue from charring, which in turn maychange the effective wavelength. Second region 644 is generally theportion of antenna 640 which is in contact with the tissue surrounding atumor or lesion to be ablated. This region 644 typically becomes hotfrom ohmic heating and some conductive heating from first region 642. Itmay be desirable to allow second region 644 to heat up in certain tissueregions where coagulation of the insertion tract may be desirable.However, it may also be desirable to cool this region 644 in otherapplications to protect surrounding sensitive tissue structures fromheat damage. Finally, third region 646 is generally the portion ofantenna 640 which comes into contact with the skin of a patient. Thisregion 646 typically heats up because of ohmic heating and it isgenerally desirable to keep this region cool when used in percutaneousor laparoscopic procedures to prevent heat damage to the skin surface.In other procedures, such as in applications where lesions are locateddeep within the tissue, it may be desirable to allow region 646 tobecome heated to allow for the coagulation of the insertion tract.

Accordingly, a multi-zone cooling assembly 650, such as the variationshown in FIG. 25, may be utilized to take advantage of optionallycooling multiple regions along the length of a microwave antenna.Cooling jacket 652 may surround the length of microwave antenna 660 anddefine a smooth outer surface for insertion into tissue. The interior ofcooling jacket 652 may define a distal first cooling region 654, secondcooling region 656, and a proximal third cooling region 658. Thesecooling regions 654, 656, 658 may correspond to and envelope the variousregions of antenna 660, e.g., first region 662 may be positioned withinfirst cooling region 654, second region 664 may be positioned withinsecond cooling region 656, and third region 666 may be positioned withinthird cooling region 658. Each of the cooling regions 654, 656, 658 maybe divided from one another when antenna 660 is positioned withincooling jacket 652 via, e.g., electrically insulative gaskets such asrubber or polymers, to prevent fluid communication between the adjacentcooling regions. For instance, first divider 680 may separate first andsecond cooling regions 654, 656; second divider 682 may separate secondand third cooling regions 656, 658; and third divider 684 may separatethird cooling region 658 from the remainder of cooling jacket 652.

Each individual cooling region may thus be maintained at a differentcooling rate than from an adjacent cooling region, depending upon thedesired cooling profile. To maintain the differential cooling regions,any of the various cooling methods described herein may be utilized; inparticular, each cooling region may utilize its own fluid inlet andoutlet tubes. For instance, as shown in the figure, first cooling region654 may have a first inlet tube 668 and first outlet tube 670; secondcooling region 656 may have a second inlet tube 672 and second outlettube 674; and third cooling region 658 may have a third inlet tube 676and third outlet tube 678. Each pair of inlet and outlet tubes may beconnected to separate pumps or they may be connected to a common pumpwith individually controlled valves for maintaining each cooling regionat a different flow rate, if desired. The number of cooling regions ismerely illustrative in this example and is not intended to be limiting.

FIG. 26A shows yet another variation in which the diameters of the innerconductor may be modified so that proximal portions of the innerconductor function as a heat sink to facilitate conductive cooling ofthe microwave antenna. Multi-diameter cable assembly 690 may comprise aninner conductor assembly 692 having a proximal portion 694 with a firstdiameter and a distal portion 696 with a second diameter smaller thanthe first diameter. The two portions 694, 696 may be joined via atapered portion 698. The inner conductor assembly 692 may be surroundedby outer conductor 700, which may also similarly taper from a firstportion having a diameter, e.g., 0.141 inches, down into a secondportion having a diameter, e.g., 0.070 inches, smaller that the firstportion to facilitate insertion into tissue. This dual-diameter innerconductor assembly may not only increase the pushability of the antennaportion into the tissue, but may also allow proximal portion 694 tofunction as a heat sink and to help conduct heat away proximally fromthe radiating portion. Moreover, having a larger cable helps to improvethe power handling capabilities which in turn helps to facilitate adecrease in the generation of high temperatures which may be harmful tohealthy tissue. The tapered portion 698 may be created, e.g., bysoldering the two portions 694, 696 together.

FIGS. 26B and 26C show cross-sectional side views of optionaltransitional diameters which may be utilized for the inner conductors.As shown in FIG. 26B, first portion 702 may have a standard diameter of,e.g., 0.141 inches, while second distal portion 704 may transition downto a portion having a diameter of, e.g., 0.070 inches. FIG. 26C showsanother example where first portion 702 may transition down to a seconddistal portion 706 having a diameter of, e.g., 0.085 inches. Othervariations may utilize other diameters and these examples are shown forillustrative purposes only.

An example of the cooling capacity of some of the cooling variationsdescribed above is shown in the corresponding plots in FIGS. 27 and 28.FIG. 27 shows a plot 710 over time of the heating which may occur in amicrowave antenna which is uncooled. The temperature measurements weretaken along a middle portion of a microwave antenna having a diameter ofabout 0.047 inches. At 60 W of power, the measured temperature reachesapproximately 100° C. in less than 9 seconds. FIG. 28 shows an examplein plot 720 of the cooling capacity of the same microwave antennautilizing a cooling sheath as shown in FIGS. 13A to 13C, as describedabove. With the power initially off, temperature measurements were takenon the surface of the cooling sheath above the same location wheremeasurements were taken on the microwave antenna. Slope 722 indicatesantenna heating at 60 W of power with no cooling fluid being pumpedthrough the sheath. Slope 724 indicates where the cooling fluid is beingcirculated through the sheath. Measurements indicated that thetemperature of the antenna returned to normal levels within 6-8 secondsfrom when the cooling fluid was circulated. Cooling fluid was then shutoff and a temperature rise 726 may be seen again. Slope 728 indicatesagain where the fluid is restarted to circulate within the sheath.

This invention has been described and specific examples of the inventionhave been portrayed. The use of those specifics is not intended to limitthe invention in any way. It is also contemplated that combinations offeatures between various examples disclosed above may be utilized withone another in other variations. Additionally, to the extent there arevariations of the invention which are within the spirit of thedisclosure and yet are equivalent to the inventions found in the claims,it is our intent that this patent will cover those variations as well.

We claim:
 1. A microwave antenna assembly, comprising: a feedlineincluding a first conductor; a radiating portion extending from a distalend of the feedline; and a cooling system including: a first tubularmember extending along a portion of a length of the first conductor anddefining a first channel for delivering fluid and having an end; and asecond tubular member coaxially aligned with the first conductor, thesecond tubular member extending along a portion of a length of the firsttubular member and defining a second channel in fluid communication withthe first channel such that fluid is exchangeable therebetween, thefirst conductor and the end of the first tubular member being disposedwithin the second channel, and a longitudinal axis defined by the secondtubular member being laterally offset from a longitudinal axis definedby the first tubular member.
 2. The microwave antenna assembly of claim1, wherein the first tubular member of the cooling system extends over aportion of the radiating portion.
 3. The microwave antenna assembly ofclaim 1, wherein the feedline further includes a second conductor and adielectric material, the dielectric material surrounds a portion of thesecond conductor, and the first conductor surrounds a portion of thedielectric material.
 4. The microwave antenna assembly of claim 1,wherein the second tubular member further includes a tapered distal endterminating in a tip.
 5. The microwave antenna assembly of claim 1,wherein a distal end of the radiating portion extends beyond a distalend of the first tubular member.
 6. The microwave antenna assembly ofclaim 1, further comprising a fluid source, wherein the first tubularmember and the second tubular member each define a conduit in fluidcommunication with the fluid source to provide fluid to the first andsecond channels.
 7. The microwave antenna assembly of claim 6, whereinthe fluid source is configured to generate one of a positive pressure ora negative pressure within at least one of the first or second channels.8. The microwave antenna assembly of claim 1, wherein the radiatingportion defines a curved profile and an ablation region therein.
 9. Themicrowave antenna assembly of claim 1, wherein the radiating portiondefines a straight probe profile.
 10. The microwave antenna assembly ofclaim 1, wherein the cooling system further includes a temperaturesensor configured to sense a temperature of at least one of the firstconductor or the radiating portion.
 11. The microwave antenna assemblyof claim 1, wherein the second channel is defined between the secondtubular member and the first conductor, and the first tubular member isinterposed therebetween.